CSM-Java Programming-I Spring,2005 Fundamental Data Types Lesson - 2

CSM-Java Programming-I Lesson-1 Objectives Review of last class. Identifiers and primitive data types. Operators.

CSM-Java Programming-I Lesson-1 Identifiers Java identifiers are used for names of variables, constants and labels. They must start with a letter, a currency symbol or underscore (_) followed by letters, digits or both. Java language keywords cannot be used as identifiers. Eg: int, private, void, new, for…

CSM-Java Programming-I Lesson-1 Primitive Types boolen either true or false char 16-bits byte 8-bits short 16-bits int 32-bits long 64-bits float 32-bits double 64-bits

CSM-Java Programming-I Lesson-1 Literals A literal is a constant value that may be assigned to a primitive type. Boolean – true and false Integer – Integer constants are strings of octal, decimal or hexadecimal digits. E.g.: 29-decimal 035-octal 0x1D, 0X1d-hexadecimal Suffix a L to indicate a long (64 bit) literal)

CSM-Java Programming-I Lesson-1 Literals Floating-Point – Floating point literals are expressed as decimal numbers. E.g.: 18., 1.8e1,.18E2 all denote the same number. A floating-point literal with no F or D suffix defaults to double type. Character – Character literals appear between single quotes. E.g.: ‘Q’.

CSM-Java Programming-I Lesson-1 Literals Character – Certain special characters can be represented by an escape sequence. E.g.: \n for newline, \t for tab, \b for backspace. Strings – String literals appear between double quotes. E.g.: “Hi”. A string literal references an object of type String.

CSM-Java Programming-I Lesson-1 Strings Strings – String is a sequence of characters. Strings are objects of the String class. The number of characters in a string is called the length of the string. Eg: int n = message.length(); Strings can be concatenated, by using the + operator. String name = “dave”; String message = “Hello, “ + name; Whenever one of the arguments of the + operator is a string, the other argument is converted to a string.

CSM-Java Programming-I Lesson-1 Strings If a string contains the digits of a number, use the Integer.parseInt or Double.parseDouble method to obtain the number value. Use the substring() method to extract a part of a string. Eg: String greeting = “Hello World!”; String sub = greeting.substring(0,4); // sub = “Hell” String positions are counted starting with 0.

CSM-Java Programming-I Lesson-1 final Keyword Any number that is not completely self- explanatory should be declared as a named constant. A final variable is a constant. Once its value has been set, it cannot be changed. Use named constants to make your programs easier to read and maintain. Eg: final int DAYS_PER_YEAR = 365;

CSM-Java Programming-I Lesson-1 static Keyword Java numbers are not objects, so you cannot invoke a method on a number. Eg: To calculate sqrt or power. A static method does not operate on an object. Eg: Math.sqrt(x); Math.round(y);

CSM-Java Programming-I Lesson-1 Type Conversion When an assignment is made to a variable, the types of either side of the assignment must be compatible. Eg 1: double total = “a lot”; //Error Eg 2: int dollars = 2; double total = dollars; // Correct – This is called implicit conversion. Eg 3: double dollars = 2; int total = dollars; // Error

CSM-Java Programming-I Lesson-1 Type Conversion Eg 3: double dollars = 2; int total = dollars; // Error Casting: You must convert the floating-point value to integer with a cast. (type) expression; int total = (int) dollars;

CSM-Java Programming-I Lesson-1 Type Conversion Loss of Information Eg 1: double total = 13.75; int pennies = (int)(total *100); Use the Math.round() method to round a floating-point number to the nearest integer to avoid the loss of information.

CSM-Java Programming-I Lesson-1 Operators Arithmetic Operators +, -, *, /, % (remainder) If both the arguments of the / operator are integers, the result is an integer and the remainder is discarded. Eg: 7/4 = 1; 3 is discarded.

CSM-Java Programming-I Lesson-1 Operators Arithmetic Operators +, -, *, /, % (remainder) Eg: 7.0/4.0, 7/4.0, 7.0/4 all yield 1.75 The % operator computes the remainder of a division. Eg: 7 % 4 = 3

CSM-Java Programming-I Lesson-1 Common Errors Integer Division Eg: int s1 = 5; int s2 = 6; double avg = (s1 + s2) / 3; // Error double avg = (s1 + s2) / 3.0; //Correct Unbalanced Parentheses 1.5 * ((- (b – Math.sqrt(b*b – 4*a*c)) / (2*a))

CSM-Java Programming-I Lesson-1 Operators Increment and decrement Operators ++, -- i++ is equivalent to i= i+1 Increment and decrement operators can be either prefix of postfix operators (they can appear either before or after what they operate on).

CSM-Java Programming-I Lesson-1 Increment and decrement Operators If increment or decrement operators appear before (prefix), the operation is applied before the value of the expression is returned. If increment or decrement operators appear after (postfix), the operation is applied after the value of the expression is used.

CSM-Java Programming-I Lesson-1 Example: Increment and decrement Operators public class Ex1 { public static void main(String args[]) { int x = 10; System.out.println(++x); System.out.println(x++); System.out.println(x); }

CSM-Java Programming-I Lesson-1 Relational and Equality Operators > greater than >= greater than or equal to < less than <=less than or equal to == equal to – equality op. != not equal to – equality op. The unary operator ! Inverts a boolean; !true is same as false Equality operators opearte only on boolean values

CSM-Java Programming-I Lesson-1 Logical Operators && - conditional AND || - conditional OR

CSM-Java Programming-I Lesson-1 Example1: Logical Operators if (x && y) { if (y || z) { Do something } The inner if is executed only if both x and y are true. If x is false, y is not evaluated. The body of inner if is excecuted if either y or z is true. If y is true, z is not evaluated.

CSM-Java Programming-I Lesson-1 Ternary Operator x = (a ? b : c) is equivalent to if (a) x = b; else x = c;

CSM-Java Programming-I Lesson-1 Assignment Operator a +=10; Same as a = a+10; Same for all arithmetic operators

CSM-Java Programming-I Lesson-1 Operator Precedence The order of precedence of operators from highest to lowest is: postfix [],., (params), expr++, expr— Unary ++expr, –expr, +expr, –expr ! Multiplicative* / % Additive+ - Relational, = Equality==, != Logical AND&& Logical OR|| Ternary?: Assignment=, +=, -=, *=, /=, %=

CSM-Java Programming-I Lesson-1 Operator Precedence Operators with the same precedence appear on the same line in the table. Precedence can be overridden using parentheses Operands to the operators will be evaluated left- to-right, except for &&, ||, ?:. Eg: x+y+z. First evaluates x, then y, adds the values together, evaluates z and adds that to the previous result.